The present invention relates to a positioning arrangement in general, and more particularly to a positioning arrangement for use in a machine tool, such as a cutting or shearing machine.
There are already known various positioning arrangements which can be used for positioning a workpiece relative to a machine tool, such as a cutting or shearing machine. Such an arrangement usually includes an abutment which is mounted on an abutment carriage for movement longitudinally of an elongated rail. An arresting device is provided which arrests the abutment carriage in a selected one of a plurality of positions along the elongated rail so that the abutment is located a predetermined distance downstream of the cutting or shearing blades of the machine. In the conventional arrangements, the arresting device either includes an arresting member which frictionally engages a portion of the elongated rail, or both the arresting member and the elongated rail are formed with serrated portions which engage with one another in a plurality of discrete positions of the abutment carriage relative to the elongated rail. It will be appreciated that, in the former event, the frictional engagement does not assure with absolute certainty tha the abutment carriage will remain in its selected position for an extended period of time needed for accomplishing a series of cutting operations, particularly when the abutment carried by the abutment carriage is subjected to substantial impacts. On the other hand, the construction of the arresting device with the cooperating serrations, while preventing movement of the abutment carriage longitudinally of the rail due to the impact forces to which the abutment carriage often is subjected, does not permit arresting of the abutment carriage in any of an infinite number of positions longitudinally of the rail, but only permits arresting of the abutment carriage in a plurality of discrete positions.
The above problems are especially present, and the above considerations particularly valid, in shearing machines which are used for severing blanks from profiled elongated rods, which blanks are then to be used in forging, particularly in drop forging or swage or die forging operations. Under these circumstances, the other dimensions being given by the dimensions of other profiled elongated rods, the length of the severed-off blank determines the amount and weight of the material present in the blank. Inasmuch as the above-mentioned forging operations require that the weight of the blank be as accurate as possible, a deviation of 0.5% one way or the other being about the most that can be tolerated, it is necessary to adjust the position of the abutment relative to the shearing blades with the necessary accuracy. In such shearing machines, the abutment is located downstream of the shearing blades when considered in the direction of advancement of the elongated profiled bar or rod, the latter abutting against the abutment and thus being stopped in a predetermined position relative to the shearing blades. Since the elongated rod may have a mass of, for instance, 500 kilograms, and may abut the abutment with a speed of 0.5 meters per second, the arresting device must be so constructed as to assure that the abutment will not be displaced away from the shearing blades as a result of such impact, whether or not the latter are damped by pneumatic or hydraulic damping arrangements. To illustrate the degree of accuracy with which the positioning arrangement ought to be located and arrested with respect to the shearing blades, it is to be mentioned that, when the profiled elongated bar or rod is of a square cross-section of approximately 100 times 100 millimeters, and having a length of 100 millimeters, a length tolerance of approximately .+-.0.2 millimeters is acceptable as a rule, since under such circumstances the weight tolerance will be within acceptable limits.
It is also already knwon to utilize, in such arrangements, a manually operated clamping lever which exerts a pressing force on the elongated guide rail via a threaded spindle, but such an arrangement achieves less than satisfactory results, for the reasons mentioned above, in the arrangement of the type here under consideration, particularly as far as the exact positioning of the abutment carriage and the stability of the abutment carriage in a selected position are concerned.